簡體   English   中英

在EF Core中添加外鍵列

[英]Add Foreign Key Column In EF Core

我有一個現有的表Projects ,我想向其中添加UserId列,其中UserId是外鍵。 現在的Projects有一個名稱列表,但是我希望每個用戶都可以管理自己的項目。 我最初擁有“孤兒”是可以的,因為列表足夠小,我可以手動清理它們。

我已經更新了模型,以包含UserId和導航屬性User (可能不相關,但是此處的Entity是具有IdDateModified基類)

public class Project : Entity
{
    public string Name { get; set; }
    public Guid? UserId { get; set; } //tried this as nullable and non nullable
    public User User { get; set; }
}

我相關的映射文件是

public class ProjectMap : IEntityTypeConfiguration<Project>
{
    public void Configure(EntityTypeBuilder<Project> builder)
    {
        builder.Property(x => x.Name).IsRequired();
        builder.Property(x => x.UserId).IsRequired();

        builder.HasOne(x => x.User)
            .WithMany(x => x.Projects)
            .HasForeignKey(x => x.UserId)
            .OnDelete(DeleteBehavior.SetNull);  //I have tried numerous combinations of things here....
    }
}

我還向項目的User實體添加了導航屬性,但未對映射類進行任何更改。

public class User : Entity
{
    public string EmailAddress { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public List<Task> Tasks { get; set; }
    public List<Project> Projects { get; set; }
}

由此產生的遷移:

    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.AddColumn<Guid>(
            name: "UserId",
            table: "Projects",
            nullable: false,
            defaultValue: new Guid("00000000-0000-0000-0000-000000000000"));

        migrationBuilder.CreateIndex(
            name: "IX_Projects_UserId",
            table: "Projects",
            column: "UserId");

        migrationBuilder.AddForeignKey(
            name: "FK_Projects_Users_UserId",
            table: "Projects",
            column: "UserId",
            principalTable: "Users",
            principalColumn: "Id",
            onDelete: ReferentialAction.SetNull);
    }

運行更新數據庫時會轉換為此SQL

ALTER TABLE [Projects] ADD CONSTRAINT [FK_Projects_Users_UserId] FOREIGN KEY ([UserId]) REFERENCES [Users] ([Id]) ON DELETE SET NULL;

並因該錯誤而失敗

Cannot create the foreign key "FK_Projects_Users_UserId" with the SET NULL referential action, because one or more referencing columns are not nullable.

我究竟做錯了什么?

下面的行導致了此問題,因為您希望Project FK為空

builder.Property(x => x.UserId).IsRequired();

另外,您生成的遷移已經具有提示:

 nullable: false,

只需在您的Configure方法上刪除該行,它就可以工作。 您可能還需要通過運行Remove-Migration ,然后再次運行add-migration來刪除遷移。 這次您應該具有以下功能:

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.AlterColumn<string>(
        name: "Name",
        table: "Projects",
        nullable: false,
        oldClrType: typeof(string),
        oldNullable: true);

    migrationBuilder.AddColumn<Guid>(
        name: "UserId",
        table: "Projects",
        nullable: true);

    migrationBuilder.CreateIndex(
        name: "IX_Projects_UserId",
        table: "Projects",
        column: "UserId");

    migrationBuilder.AddForeignKey(
        name: "FK_Projects_Users_UserId",
        table: "Projects",
        column: "UserId",
        principalTable: "Users",
        principalColumn: "Id",
        onDelete: ReferentialAction.SetNull);
}

如果需要,可以通過在配置關系時顯式設置IsRequired來更具體:

private static void ConfigureProject(EntityTypeBuilder<Project> b)
{
    b.Property(x => x.Name).IsRequired();

    b.HasOne(x => x.User)
        .WithMany(x => x.Projects)
        .HasForeignKey(x => x.UserId)
        .IsRequired(false)
        .OnDelete(DeleteBehavior.SetNull);
}

即使該屬性已經可以為空,並且EF會使用其約定正確地創建它,我還是喜歡它,對於某些無需閱讀實際Project類就可以閱讀配置並了解它的人來說,它仍然很不錯。

在功能配置中,您可以指定:

builder.Property(x => x.UserId).IsRequired();

這不是說UserId不能為null嗎? 但是您希望它為空嗎?

暫無
暫無

聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.

 
粵ICP備18138465號  © 2020-2024 STACKOOM.COM